The present invention relates to a printing ink composition. More particularly, the invention is directed to a printing ink emulsion for lithographic and related printing and in which the composition is used effectively in a single-application-step printing process obviating and requirement for a separate water coat application to a non-image area of a printing plate to render that area ink-repellant.
The present invention constitutes an important improvement in both ink compositions and in the manner in which such compositions are applied in lithographic printing and in related printing such as offset printing, lithography, ect.
The art in which the present finds utility is a highly sophisticated and highly developed art in which the printing surface involved is of the type that is devoid of appreciable elevation variation, relief, or depression. This type of printing may be contrasted generally with what is known as letter press printing in which raised type or image surfaces are involved.
The general construction and composition of printing plates of the type useful in practicing the present invention are well-known in the art. Accordingly, no detailed description is deemed to be required herein. A description of lithographic printing, including a summary of the various techniques involved is found in Parkinson U.S. Pat. No. 4,045,232, and the entire disclosure of that patent is hereby specifically incorporated herein by reference, to the extent it is not inconsistent herewith.
The various methods which have been employed to apply an image to be imprinted onto the surface of the plate are described in the cited reference, which also includes a description of the preparation of the plates themselves. The method by which the printing plate is prepared for use does not constitute an element of the present invention. Rather, the invention lines in the provision of a unique printing ink composition of the type which may be used without the need to apply a water coating to the surface of the printing plate to define a non-image area which is thus rendered ink-repellant.
Various techniques and compositions have been suggested for use in lithographic type printing techniques so as to obviate the need to apply a water coating to the surface of the printing plate. Among liquid preparations which have been proposed as treating media to be applied to non-image areas of printing plates are solutions containing particular salts and glycerin. Such solutions have been found objectionable for various reasons including instability in use and as being objectionably hygroscopic. Moreover, it was necessary that the application of the solutions be frequently repeated, preferably with each successive inking of the printing plate or roll.
The desirability of being able to use an ink composition containing agents for treating both the image producing area and the non-print area, simultaneously, and from a single solution, has also been recognized. For the most part, compositions purporting to function in this manner have been found to be objectionable due to the lack of satisfactory definition and because of impaired toning. Such compositions have also failed to demonstrate the type of stability and reliability required for practical commercial use. It is, therefore, a principal aim of the present invention to proved a "single composition" printing ink for a "single application" which is effective to obviate the need for a separate water coating step in a lithographic type printing operation, and in which the composition obviates the deficiencies and shortcomings of prior art preparations and techniques.